1. Field of the Invention
The invention relates to a method for housing sensors in a package and, in particular, housing chemical sensors, flow sensors or optical sensors in a synthetic package.
2. Prior Art
Chemical sensors, like flow sensors or optical sensors, may be manufactured already in an integrated form in a cost-effective manner and at a high precision by conventional chip manufacturing processes. However, such IC sensors or chip sensors subsequently had to be incorporated in a package, which involved cumbersome assembly work, whereby the package, as a rule, was either screwed or glued and the connections to the sensors had to be led out of the package in a suitable manner. This applied not only to the electrical connections, but, in the case of chemical sensors, flow rate sensors or optical sensors, naturally also to line connections or optical fiber connections, which called for appropriate additional adaptation work of the packages. Thus, in the production of such sensors, incorporation in a package constituted a cost-determining factor for mass production.
The invention aims to provide a method of the initially defined kind, by which the assembly work involved can be substantially reduced and the necessary connections can, at the same time, be provided in a cost-effective manner by a few method steps. To solve this object, the method according to the invention essentially consists in that, in a first method step, the active sensor surface of a semiconductor or IC sensor is provided with a cap forming a hollow space above the active sensor surface and the sensor is connected with contacts and bond wires, that, after this, the package is formed by molding, in particular injection molding, and that, in a third method step or simultaneously with the second method step, the hollow space formed above the active sensor surface is opened. In principle, chip molding with a suitable molding compound is known for many electronic components. Yet, none of the known methods is suitable for sensors which require to be in contact with the atmosphere, since after molding the sensor will no longer be accessible without cumbersome aftertreatment and the risk of damage to the sensor cannot be excluded in case of subsequent adaptation work. Due to the fact that, according to the invention, the active sensor surface of a semiconductor or IC sensor is provided with a cap forming a hollow space above the active sensor surface in a fist method step, the respective active sensor surface is kept free of the molding compound to be applied subsequently. The provision of bond wires as is common in chip manufacturing may be accomplished in a simple manner by conventional means, wherein, by a subsequent molding procedure, in particular an injection molding procedure, a finished component already comprising all electrical contacts is immediately provided. Thus, it merely has to be safeguarded that the active sensor surface in a suitable manner will again be in contact with the environment, to which end the hollow space is mechanically opened either during the second method step simultaneously with the casting-on or molding of the package or following this second method step. The opening of the hollow space in a third method step carried out subsequently is preferred to the simultaneous formation of the opening not the least because the simultaneous opening of the hollow space requires that the wall of the cap defining the hollow space be pierced immediately upon closure of the mold or injection mold, respectively. Since the injection molding compound, as a rule, has not set at that point of time, this will cause the previously positioned sensor to be displaced within the molding compound if no suitable abutment is provided on the opposite side. If injection molding is performed at an accordingly higher pressure, it will also have to be ensured in such a case that the mold will tightly sever the cap in order to prevent molding compound from being pressed into the hollow space. In the context of the method according to the invention, it is, therefore, advantageously proceeded such that the hollow space is opened by sawing and/or drilling after the at least partial setting of the molding compound.
In a particularly simple manner, the package may be made of suitable synthetics, a number of synthetics having proved to be suitable in semiconductor technology.
If an optical sensor is employed, the hollow space advantageously may be opened by drilling, whereupon an optical fiber is introduced into the opened hollow space.
In order to ensure the simultaneous formation of the electrical contacts with a view to inserting such a sensor provided with a package into a base or an appropriately prepared printed circuit board, it may advantageously be proceeded in a manner that the bond wires are connected with a frame including contact pins and that the frame is embbed in the molding compound leaving free the contact pins.